The present invention relates to a method of mounting the support for a cathode in a hole of an insulating part against one side of which the support rests with a bulge. Such cathode structures are used, for example, in electron-gun systems of picture tubes. Such a cathode, illustrated in FIG. 1 of the accompanying drawing, is shown, for example, in the figure of German Auslegeschrift (DE-AS) No. 23 13 911, and its principle is described in an article by M. Tischer, "Die Oxidkathode in der Bildrohre", periodical "Funkschau", 1967, No. 21, pp. 675-677
From British Pat. No. 725,250 it is known to pass a tubular cathode through a hole in an insulating disk until the disk is located against a bulge on the cathode, and to subsequently bend over the projecting portion of the cathode along its entire circumference. With the progress in cathode-ray tube technology, ever shorter warm-up times have been required. Instead of mounting the cathode directly in the insulating disk, it is, therefore, common practice to connect the cathode to the insulating disk by means of a cathode support, keeping heat conduction to a minimum. This step results in a considerable reduction in warm-up time, which is why such cathodes are also called "fast warm-up cathodes".
In conventional designs, the cathode support is mounted in the hole of the insulating part, usually a ceramic material, by cold riveting. That portion of the cathode support which projects beyond the hole is bent over by means of a punch, and at the same time the cathode support is slightly upset so as to be firmly fixed in the hole. The material for the cathode and cathode support is so chosen as to insure optimum workability during riveting.
To further reduce the warm-up time, the heat capacity of the cathode support and the thermal conductivity of the material of which the support is made have been further decreased. In the case of wall thicknesses of &lt;0.1 mm and/or if a hard-to-deform material such as Ni 80 Cr 20 is used, longitudinal cracks are formed in the bending area which greatly reduce the stability of the mount. When forming the bulge with which the cathode support rests against the insulating part, similar problems arise, but it is readily possible to take special measures during the production of these semi-fabricated components to prevent cracking, such as very high temperatures in the area where the bulge is formed.
Cathode supports having such thin walls and made of hard-to-deform materials such as the aforementioned Ni 80 Cr 20 are increasingly used in so-called fast warm-up cathodes, in which the cathode support should have a low thermal conductivity and a low thermal capacity.
In addition, cathode supports not securely held in the ceramic part result in unstable cathode temperatures because of the varying heat transfer.
The object of the invention is to provide a method whereby very thin-walled cathode supports, even if made of hard-to-deform material, can be mounted without any cracks forming in the bent portion and which simultaneously ensures that the cathode support is securely held in the opening of the ceramic disk.
This object is achieved by the means set forth in the claims.
Besides permitting the use of materials which are difficult to work or have a small wall thickness, the method claimed has the advantage of considerably stabilizing the cathode temperature as a result of a well reproducible heat transfer from the cathode support to the ceramic material. Even at high operating temperatures, the cathode support will no longer come loose.